Practically every camera that is available today includes an exposure counter. The exposure counter provides a visible indication of the number of film frames that remain available to be exposed on a filmstrip in the camera, i.e. the current number of exposures that can be made on the filmstrip. Alternatively, the exposure counter can provide a visible indication of the number of film frames actually exposed on the filmstrip, i.e. the number of exposures already made. In either case, the exposure counter includes a numerical scale of successive exposure count indicia that are evenly spaced from one another. The scale of indicia at least range from the number "1" which indicates either that only one frame remains available to be exposed on the filmstrip, or only one frame has been actually exposed, to a higher number which is the maximum number of exposures, for example "15", "24" or "40". Each time the filmstrip is advanced one frame increment, the exposure counter undergoes an indicia change equivalent to one frame, which can be one less or one more than the previous number.
Early prior art U.S. Pat. No. 1,642,818 issued Sep. 20, 1927 discloses a dual wheel type of exposure counter comprising a count-by-unit counter wheel having ten evenly spaced units and a single actuating pawl, and a count-by-tenths counter wheel having ten evenly spaced units which are the same as the ten units of the unit counter wheel and respective peripheral teeth which correspond to the ten units of the tenths counter wheel. The actuating pawl on the unit counter wheel successively engages the peripheral teeth on the tenths counter wheel to rotate the tenths counter wheel to change by one unit in response to each rotation of the unit counter wheel to change by ten units. The ten units on the unit counter wheel and the ten units on the tenths counter wheel are designated "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" on respective top sides of the two counter wheels. The unit counter wheel is incrementally rotated ten times to move the designations "1", "2", "3", "4", "5", "6", "7", "8", "9", "0" on the unit counter wheel successively into and out of a counter window in the housing of the camera. When the designation "0" on the unit counter wheel is moved into the counter window, following movement of the designation "9" on the unit wheel out of the counter window, the actuating pawl on the unit counter wheel engages one of the peripheral teeth on the tenths counter wheel to incrementally rotate the tenths counter wheel to move one of the designations "0", "1", "2", "3", "4", "5", "6", "7", "8" "9" on the tenths counter wheel out of the counter window and move the next higher designation on the tenths counter wheel into the counter window. This can provide a frame count from "01" to "99", which is particularly useful when a relatively long length of film is used in the camera. However, a possible problem is that the engagement of the actuating pawl on the unit counter wheel with any one of the peripheral teeth on the tenths counter wheel is momentary, rather than continuous. Consequently, when the actuating pawl is not engaged with one of the peripheral teeth, a mechanical shock to the exposure counter, for example should the camera be dropped, could move the tenths counter wheel to be out of count.
Later prior art U.S. Pat. No. 5,809,351 issued Sep. 15, 1998 discloses a dual wheel exposure counter comprising a tenths counter wheel having a series of six evenly spaced units and six evenly spaced actuated members, and a unit counter wheel having a series of ten evenly spaced units and a single actuating member which successively actuates the actuated members to rotate the tenths counter wheel to change by one unit in response to each rotation of the unit counter wheel to change by ten units. The six units on the tenths counter wheel are designated "5", "4", "3", "2", "1", "0", and the ten units on the units counter wheel are designated "9", "8", "7", "6", "5", "4", "3", "2", "1", "0". The unit counter wheel includes an opposed-end concentric channel having an opening between opposite ends of the channel. The single actuating member of the unit counter wheel constitutes a protuberance which is positioned in the opening to leave respective ingress and egress spaces in the opening between the protuberance and the opposite ends of the channel. The actuated members are positioned on the tenths counter wheel for the protuberance to drive one of the actuated members out of the channel through the egress space to rotate the tenths counter wheel to change by one unit and move another of the actuated members into the channel through the ingress space, each time the unit counter wheel is rotated to change by ten units. The fact that one of the actuating members is always in the channel serves to prevent any unintended rotation of the tenths counter wheel with respect to the unit counter wheel.